Michelsen bounced back after failing to convert six set points in the opening set, finishing in two hours, 40 minutes. He saved seven of 10 break points.
No. 7 seed Nuno Borges of Portugal, the only other seeded player in action, outlasted Italy's Luciano Darderi 5-7, 6-3, 7-5. Belgium's Zizou Bergs defeated New Zealand's Isaac Becroft 6-3, 7-5 and Spain's Roberto Carballes Baena held off Germany's Daniel Altmaier 6-3, 3-6, 7-5.
Adelaide International
Canada's Denis Shapovalov struck nine aces and won 31 of 32 points on his first serve in a swift 6-3, 6-4 victory over No. 9 seed Zhizhen Zhang of China in Australia.
Shapovalov never faced a break point in the 67-minute win as he breezed into the second round.
Australians Thanasi Kokkinakis and Christopher O'Connell also advanced. Kokkinakis was a 6-3, 3-6, 6-3 winner over Japan's Yoshihito Nishioka and O'Connell posted a 7-5, 7-6(5) win over France's Arthur Rinderknech. Alejandro Davidovich Fokina eliminated fellow Spaniard Roberto Bautista Agut 7-5, 6-2.